The present invention relates to a disk apparatus, and in particular to a sector address generation method in which information on defects of tracks to be accessed by a head can be detected with a smaller number of times of accessing, without depending on their storage locations.
Recently, a disk apparatus is rapidly becoming smaller-sized, faster, more sophisticated and cheaper. In particular, there is a tendency to become larger in storage capacity, so that a unit area recording density is improved to be more than 10 Gbit per one inch square. Such a high-density storage generates many failure-generating sectors, which can not be used as sectors. The number of defective sectors of a storage capacity is less than about 0.1% at maximum. A hot-selling 3.5-inch disk apparatus has a capacity of about 20 GB, and the maximum number of defective sectors is:(20 GB×0.1%)/512 Bytes=about 40,000 sectors.At present, recording density of a disk apparatus is increased at a pace that capacity is doubled in a year. Thus, three years later, the number of defective sectors will exceed 150,000 sectors. A disk apparatus reads and writes data from a host, while performing processing in which defective sectors are avoided as unusable sectors. This processing is called defective sector processing.
The defective sector processing will be described in detail referring to a diagram of FIG. 32 explaining conversion of a host logical number to a disk physical number, and referring to a sector allocation map of FIG. 7 for sectors including defective ones. FIG. 32 is a diagram showing a relation between a number designated by a host and a physical number indicating a physical location. The host sends a disk apparatus designation of a sector in terms of a host logical CHS number 3201, which is a Cylinder-Head-Sector number (hereinafter, referred to as a CHS number) in the disk apparatus as seen from the host, or in terms of a host logical LBA number 3205, which is a Logical Block Address number (hereinafter, referred to as an LBA number) simply as a serial number.
Here, a host logical CHS number 3201 consists of a host logical head number 3202, a host logical cylinder number 3203, and a host logical sector number 3204. Further, in the case of a host logical LBA number, a host logical LBA number [27:0] consists of three LBA numbers 3206, 3207, and 3208.
On the side of the disk apparatus, an MPU contained in the disk apparatus reads the logical CHS number or the logical LBA number set by the host, to specify an actual sector number. Or, the actual sector number may be specified by a hardware conversion unit. This result becomes a disk physical CHS number 3209. This disk physical CHS number 3209 consists of a disk physical head number 3210, a disk physical cylinder number 3211, and a disk physical sector number 3212. Using a pair of disk physical head number 3210 and disk physical cylinder number 3211, a magnetic head can be located. This disk physical CHS number Indicates an actual location where the host wishes to read or write. Thus, the sector concerned is found based on this number, to read or write data. [27:0] indicates the host LBA number from bit0 to bit27, namely 28 bit bus width.
FIG. 7 shows a sector allocation map. A disk apparatus records data into sectors on a medium 701. As an ordinary technique of increasing its capacity, the medium utilizes Zone Bit Recording. FIG. 7 shows a case of three zones, i.e., ZONE0702, ZONE1703 and ZONE2704. Within a zone, there are a plurality of tracks 706-710, each consisting of a plurality of sectors in a circumference. Here, in FIG. 7, the reference numerals 706-710 refer to actual tracks within the ZONE1. One track contains A+1 sectors 0−A (A+1 sectors/track), and the ZONE1 contains n+1 tracks, i.e., track m—track m+n (n+1 tracks/zone), which a user can handle. Further, the figure shows that a track L 710 is a substitute track used for replacing a defect sector in the same ZONE1.
Further, the figure shows a case where, between adjacent tracks, there is provided a skew for processing the next sector, such that the head is located at a leading sector in the next track just when the moving time of the head is finished after the head processed the last sector in the current track. FIG. 7 shows a case where the skew value is 2 sectors. Although a physical sector number is thus assigned to each sector, there exist some defective sectors that can not be used, among the sectors. A number of such a sector should be replaced by a number of a normal sector. As a method of replacing, there are two methods, i.e., a slip processing 711, where sectors are shifted one by one, and a skip processing 712, where a defective sector is replaced by another area. Accordingly, in order to specify a sector, it is necessary to take slips or skips into consideration to specify a disk physical number (called a disk physical CHS number) allocated from the top of the disk apparatus.
Using the MPU, the disk apparatus obtains a disk physical CHS number from a host logical CHS (LBA) number designated by the host. Then, after the head is positioned at the track concerned, the disk apparatus performs sector number control, utilizing defect control information (defect management information) for performing the slip or skip processing for that track. For example, in the sector allocation map shown in FIG. 7, it is assumed that the sector designated by the host exists on the track m+n. The track m+n is specified in the manner explained in the above-mentioned FIG. 32. For example, it is assumed that read or write is performed from the sector (A−2n−4). After the head reaches the sector (A−2n−4), access processing to the sector (A−2n−4) is performed. Next, when the sector (A−2n−3) and the following should be accessed, it can be known from defect management information (defect control information) prepared in advance in the apparatus that two consecutive sectors including the sector (A−2n−3) are defective sectors, and they are skip sectors assigned with substitutes. It is seen that this sector (A−2n−3) has a substitute sector on the track L, and accordingly, the sector in question on the track L is accessed. Finishing the skip processing, the access processing is returned to the sector (A−2n−1) and the following on the original track m+n. When the processing is finished until the sector (A−2n+1), it is seen from the defect management information that the sector (A−2n+2) should be subjected to slip processing. Accordingly, no processing is performed on this sector, moving to the next sector (A−2n+3). Thus, to perform defect processing, it is necessary to find information on a track that is to be currently accessed by the head, searching the defect management information prepared in advance.
As capacity of a disk apparatus becomes larger, the number of defective sectors per apparatus becomes larger. This causes deterioration of performance of the apparatus, since time for searching defect control information on the disk apparatus increases as the defect management information increases. As a measure against deterioration of performance, may be mentioned a technique disclosed in Japanese Unexamined Patent Laid-Open No. 11-7730. This conventional technique achieves high-speed defect processing, by preparing information that indicates existence of defects for each track, pointer information that indicates where is management information indicating defect sector information on the defective track corresponding to the above-mentioned information, and the management information mentioned.